The invention relates to a ground clamp for a welding apparatus. The ground clamp comprises a fastening screw rotatable in a body and a counter jaw formed in said body, said fastening screw and said jaw together forming a screw clamp by means of which the ground clamp is fastened to a workpiece.
Prior ground clamps for a welding apparatus are fastened to a workpiece either by means of a spring or by means of a screw. The lack of press force is one disadvantage of ground clamps provided with a spring, and this lack is solely due to the structure of the ground clamp. Even a rigid spring is made inoperative by a small amount of welding slag. As a result, no proper contact can be obtained with the workpiece. In principle, a ground clamp provided with a screw provides a greater press force, the ground clamp according to the invention being of this particular type. However, the connection of the ground cable and the screw are so positioned with respect to each other in this type of ground clamps that a sufficient press force cannot be obtained. In some of these clamps, the poor contact between the workpiece and the ground clamp is also due to the fact that the jaws of these clamps are cogged or rounded so that their contact surfaces are small. On the other hand, prior ground clamps have drawbacks in the connection between the cable and the body of the clamp. The cable is liable to fracture at the connecting point, as a result of which the cable strands are broken.
Especially, the poor contact between the clamp and the workpiece, which is due to the low press force and the small contact surfaces, and also the broken cable strands cause the prior ground clamps to be heated up much earlier than the welding current obtains the value for which the clamps in principle are dimensioned. On account of this they cannot be operated with their full nominal current. Due to the insufficient press force in particular, but possibly also due to the broken cable strands or the weak cable connection, sudden variations occur in the welding current at the working site when a person passing by accidentally kicks the ground cable. This sudden change in the contact between the ground cable and the workpiece causes a change in the welding current, which change, in turn, affects adversely the welding result.
As appears from the above, prior ground clamps have structural disadvantages on account of which they are not reliable in operation and cannot conduct sufficiently current in proportion to their size. The disadvantages are due to the fact that the contact between the workpiece and the ground cable in these clamps is not sufficiently good to guarantee an even flow of the electrical current.